The present invention relates generally to the field of fault sensing and fault indicating apparatus. More particularly the invention relates to faulted circuit detecting apparatus having a sensing device located on or adjacent to monitored conductors of a distribution network. Still more particularly the invention relates to engagement devices employed to releasably attach the fault sensing apparatus to a monitored conductor.
Fault detectors of various types have been employed for detecting faults in electrical power distribution networks and for providing visual indication that such a fault has been detected. Such detectors commonly include a sensor portion, which is located adjacent to or positioned about a load carrying conductor in the power distribution network, and an indicator which indicates the presence or absence of a fault in the circuit. The sensor is typically an encircling looped device which is clamped directly over the conductor to be monitored. The loop may be loosely affixed over the conductor, or tightly pulled thereover. An indicator is communicatively connected to the sensor portion and is often mounted at a remote location with respect to the sensor so as to provide a more convenient observation point for workmen. Upon receipt of a signal from the sensor that a fault of a predetermined magnitude has occurred, the indicator displays a visual indication that a fault or disturbance has been detected in the monitored circuit.
Fault sensors operate through the application of a basic physical principle that current passing through a conductor will create a magnetic field about the conductor that is proportional to the magnitude of the current flowing through the conductor. By placing an inductive device in the magnetic field, a current will be induced in the inductive device when the device is interconnected into a circuit of the faulted circuit detector. In this manner, a fault current in the monitored conductor can be detected, as the current in the detector circuit will increase proportionally with that in the monitored conductor when a fault circuit passes through the monitored conductor.
Various apparatus have been used to attach the sensor of a faulted circuit detector into or onto the distribution circuit that is to be monitored. For example, U.S. Pat. No. 4,795,982 discusses the application of a faulted circuit indicator to a plug-in elbow connector, wherein the elbow includes a specialized aperture for receiving the fault sensing device. Likewise, U.S. Pat. No. 4,045,726 discusses an elbow mounted faulted circuit detector. In both instances, the electric distribution network must include a specialized component which is modified to accept the fault detector.
U.S. Pat. No. 4,881,028 discusses the application of a magnetic loop, disposed around a monitored conductor, as a means of determining the presence of a fault in the conductor. The reference does not disclose how the loop is to be placed over the conductor.
A variety of electrical testing apparatus also uses the magnetic field effect of the current passing through conductors to determine the voltage and amperage being drawn by electrical equipment such as motors. Such testing equipment is intended for light duty use, in instances where the operator can safely physically touch the insulated conductor which is being evaluated, without danger of shock or other harm. The detector of such testing apparatus is positioned adjacent to the insulated conductor that is to be evaluated, and a pair of jaws are articulated over and around the conductor being evaluated. The jaws of the detector form an aperture which is substantially larger than the diameter of the conductor. The detector is held in the operator's hand, and the jaws are articulated by a manually operated lever controlled by the operator. Electronics in the testing device yield a digital or analog indication of the voltage and amperage in the monitored conductor during operation of the motor or other current drawing equipment comprising the load on the circuit.
A variety of faulted circuit indicating apparatus has been used in the past, which must be applied to the monitored conductor while the conductor is in an un-energized condition. That is particularly disadvantageous, because it requires that the circuit in which the conductor is located be de-energized, thereby cutting off the power in the circuit to the end users. Additionally, any time that type of prior art apparatus is removed or replaced, the circuit must be de-energized. This is a time consuming process for the linesman, and inconveniences power users.
Another problem with many types of prior art faulted circuit indicating devices is that they are not easily removable once installed, in the event the operator wishes to install the indicator at another location. For example, some types of prior art devices are installed with tie wraps which must be cut to remove the device from the conductor.
Faulted circuit indicating devices have also been used in the past which may be placed on a conductor while energized. For these types of devices, a hot stick is commonly employed as a means of placing the indicating apparatus on, and removing it from, the energized conductor. However, such devices as these have a common drawback in that they are not readily placeable on certain conductors due to physical constraints imposed by the structure utilizing the conductor. For example, certain conductors disposed below the heavy metal plates of some types of transformer cells are inaccessible with the hot stick mounting apparatus and faulted circuit indicating means used in the past, because such prior art hot sticks and indicators are typically unable to be angled properly with respect to one another for access to and placement on the conductors.